A variety of currently popular electronic products, such as notebook computer and personal digital assistant (PDA), are constantly developed to have a small and compact volume for users to carry them in a more convenient manner. To minimize the weight and volume of these electronic products, some conventional built-in access means, such as disk drive, hard disk, CD-ROM, etc., are now externally connected to the electronic products via connectors. However, for some electronic products, including computers, that are mounted and used in offices and homes without the need to particularly reduce their weight, users would usually externally connect the access means to these electronic products. The access means externally connected to and disorderly located nearby the electronic products are visually unpleasant and subject to unexpected disconnection from the connectors due to undesired pull of connecting cables or electrical wires thereof. An expansion unit is developed for removably accommodating the externally provided access means therein. To use any of the external access means, simply connect the electronic product to the expansion unit via engaging means, such as pins, connectors, etc., correspondingly provided on the expansion unit and the electronic product.
However, users of the electronic product connected to the expansion unit still encounter the problem of EMI caused by the electronic product during its operation. That is, the electronic product generates electromagnetic waves during its operation to interfere with normal operation of other apparatus nearby the electronic product. It is therefore tried by the inventor to develop an expansion unit for electronic product that includes EMI prevention mechanism to overcome the problem of EMI existed in most electronic products.